Presently, small fluid sample containers often comprise limited volume inserts carried within outer containers and a spring which fits between the bottom of the insert and the bottom of the container to urge the insert upwardly against a closure cap and against the downward pressure of a fluid withdrawing instrument. The insert is typically a conical bottomed inner container, from which fluid sample is withdrawn by a hypodermic needle, syringe or miniature pipette. Upward biasing of the insert and the conical shape of the internal volume of the insert permits the fine needle or pipette to be pressed into the very bottom of the insert/inner container, without damage, to assure complete withdrawal of fluid sample therefrom.
In this conventional construction, the spring tends to be difficult to assemble, as well as a source of contaminants because of its separate manufacture and handling history. Further, the insert often becomes canted within the container assembly with the spring, as a result of which, the upward biasing action of the spring is lost or becomes less effective and the fine fluid withdrawal needle or pipette is deflected before reaching the bottom of the inner container, causing needle damage and less than fully effective withdrawal of fluid from the very bottom of the inner container.